Shielded photonic integrated circuit

ABSTRACT

A light shield may be formed in photonic integrated circuit between integrated optical devices of the photonic integrated circuit. The light shield may be built by using materials already present in the photonic integrated circuit, for example the light shield may include metal walls and doped semiconductor regions. Light-emitting or light-sensitive integrated optical devices or modules of a photonic integrated circuit may be constructed with light shields integrally built in.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/963,842, filed Dec. 9, 2015, now U.S. Pat. No. 9,739,938, which ishereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to optical devices and modules, and inparticular to photonic integrated circuits.

BACKGROUND

Photonic integrated circuits include multiple optical componentsintegrated on a common substrate, typically a semiconductor substrate.The optical components may include arrays of elements such aswaveguides, splitters, couplers, interferometers, modulators, filters,etc., and may have similar or different optical processing functions.Photonic integrated circuits may be built by bonding together severaloptical, electro-optical, or optoelectronic chips. Electrical driverchips may also be attached to optoelectronic chips and electricallycoupled by solder bumps or wirebonds.

Structurally, photonic integrated circuits resemble electronicintegrated circuits, with optical waveguides for conducting opticalsignals between different optical components. Due to integratedcharacter of optical components and connections, photonic integratedcircuits may be suitable for mass production to a similar degreeintegrated electronic circuits are, potentially allowing significanteconomy of scale. Silicon-based photonic integrated circuits inparticular may benefit from a well-developed material, technological,and knowledge base of silicon-based microelectronics industry.

It may be desirable to reduce size of photonic integrated circuits tofit more circuits on a same semiconductor wafer. To achieve sizereduction, individual circuit components need to be more densely packed.There is, however, a limit on how densely the components may be packed.When distances between the components are too small, optical crosstalkmay result. The optical crosstalk occurs because light scattered fromone component may be coupled to a nearby component, impacting thatcomponent's optical performance. Amplifiers, lasers, and photodetectorsmay be particularly sensitive to optical crosstalk caused by stray lightfrom neighboring components.

One typical example of a light-scattering component is a Mach-Zehnderinterferometer of an optical modulator. When light modes in two arms ofthe Mach-Zehnder interferometer are in counter phase, a Y-junctioncombiner combining the two arms does not couple light into the outputwaveguide of the Y-junction combiner. Instead, the light is coupled intoa radiative mode, causing the light to scatter throughout the photonicintegrated circuit. Another typical example of a light-scatteringcomponent is an in-coupler of light. An in-coupler disposed near an edgeof a photonic integrated circuit may scatter light escaped the core ofan input waveguide due to an optical misalignment, imperfection of theinput optical mode, etc. The scattered light may become guided byvarious layers of the photonic integrated circuit, causing extensive“ringing”, i.e. optical crosstalk.

Thus, not only is optical crosstalk a limiting factor of miniaturizationof photonic integrated circuits, it may also be a performance-degradingfactor, and a significant design constraint. In prior-art photonicintegrated circuits, the optical components are spaced apart to reducethe effect of optical crosstalk. This increases the overall dimensionsof photonic integrated circuits, raising manufacturing costs.

SUMMARY

In accordance with an aspect of the present disclosure, a light shieldstructure may be formed between integrated optical devices of a photonicintegrated circuit. Preferably, a light shield structure is formed usingthe very materials used to build the photonic integrated circuit, i.e.the materials already present in the circuit and compatible with thematerial system of the circuit. Metal layers, metal vias, and dopedsemiconductor regions may be used to surround light-sensitive and/orlight-emitting integrated optical components or modules. Thus, a lightshield may be integrally built in.

In accordance with an aspect of the disclosure, there is provided aphotonic integrated circuit comprising a substrate, first and secondintegrated optical devices over the substrate, and a light shieldstructure between the first and second integrated optical devices. Thelight shield structure is configured to suppress optical crosstalkbetween the first and second integrated optical devices. For example,the light shield structure may include an opaque structure forsuppressing i.e. absorbing, reflecting, scattering light propagatingbetween the first and second integrated optical devices, such as a lightemitting device and a photodetector. In a preferred embodiment, theopaque structure has optical transmission of less than 10%.

In one exemplary embodiment, the opaque structure may include a firstopaque wall fully or partially surrounding the first integrated opticaldevice, e.g. on all four sides, or on three sides when the firstintegrated optical device is disposed near an edge of a photonicintegrated circuit. Openings may be provided in the first opaque wallfor optical waveguides to extend through the openings. For silicon-basedsystems, the first opaque wall may include heavily doped silicon, e.g.doped at a carrier concentration of at least 10¹⁸ cm⁻³.

In one embodiment, the opaque structure is not coplanar with the firstor second integrated optical devices. The opaque structure may include ametal structure disposed farther away from the substrate than the firstintegrated optical device, or closer to the substrate. The light shieldstructure may include a second opaque wall extending from the firstopaque wall and surrounding the first integrated optical device. Thelight shield structure may also include a photonic crystal, a plasmonicstructure, a random or semi-random scatterer, etc.

In accordance with another aspect of the disclosure, the light shieldstructure may include a dielectric layer and a channel or trenchextending through the dielectric layer from the first opaque wall andsurrounding the first integrated optical device. The channel or trenchmay be filled e.g. with metal or semiconductor, forming a second opaquewall extending from the first opaque wall. Furthermore, alight-shielding metal or semiconductor layer may be disposed over thefirst integrated optical device. The light-shielding metal orsemiconductor wall may extend to the metal or semiconductor layer, thusproviding a nearly complete integrated enclosure for the firstintegrated optical device. Similar light shielding structures may beprovided around the second integrated optical device as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described in conjunction with thedrawings, in which:

FIG. 1A is a plan view of a photonic integrated circuit of the presentdisclosure;

FIG. 1B is a side cross-sectional view of the photonic integratedcircuit of FIG. 1A, taken in a plane B-B shown in FIG. 1A;

FIG. 2 is a three-dimensional partial cut-out view of a photonicintegrated circuit including a metal light shield;

FIG. 3 is a three-dimensional partial cut-out view of a photonicintegrated circuit including a semiconductor light shield;

FIG. 4A is a frontal cross-sectional view of a shieldedwaveguide-coupled photodetector according to the present disclosure,wherein electrodes of the photodetector perform the light shieldingfunction;

FIG. 4B is a plan view of the shielded waveguide-coupled photodetectorof FIG. 4A;

FIG. 5 is a top view of a shielded waveguide Y-junction according to thepresent disclosure;

FIG. 6 is a top view of a shielded edge coupler according to the presentdisclosure;

FIG. 7 is a top view of a shielded grating coupler according to thepresent disclosure, featuring an optional shielded serpentine waveguide;

FIG. 8 is a top view of a shielded optical device, the light shieldingstructure including a Bragg grating structure;

FIG. 9 is a frontal cross-sectional view of a shielded integratedoptical device according to another aspect of the present disclosure;and

FIG. 10 is a frontal cross-sectional view of a photonic integratedcircuit of the disclosure including and an opaque wall extending betweenthe two integrated optical devices for reducing optical crosstalkbetween them.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art.

Referring to FIGS. 1A and 1B, a photonic integrated circuit 100 of thepresent disclosure includes a substrate 150, first 101 and second 102integrated optical devices over the substrate 150, and a light shieldstructure 108 between the first 101 and second 102 integrated opticaldevices. By way of a non-limiting example, the first integrated opticaldevice 101 may include a slab optical waveguide section 121 coupled toinput 151 and output 152 waveguides. The light shield structure 108 mayinclude any opaque structure, e.g. a metal structure, configured tosuppress optical crosstalk between the first 101 and second 102integrated optical devices. In the embodiment shown in FIGS. 1A and 1B,the light shield structure 108 includes a first opaque wall 131surrounding the first integrated optical device 101. An optional secondopaque wall 132 may extend from the first opaque wall 131, surroundingthe first integrated optical device 101 as shown in FIG. 1B. In oneembodiment, a metal or semiconductor shield layer (not shown forbrevity) may extend over the first integrated optical device 101 suchthat the second opaque wall 132 extends to the metal or semiconductorshield layer.

The first opaque wall 131 and/or second opaque wall 132 may include anoptically absorbing material. Furthermore, the first opaque wall 131and/or second opaque wall 132 may be at least partially reflecting,and/or scattering, to ensure that the first opaque wall 131 effectivelyfunctions as a light shield. In one embodiment, the first opaque wall131 and/or second opaque wall 132 has optical transmission of less than10%, and more preferably less than 5%, of the incoming and/or outgoingstray light.

Referring specifically to FIG. 1A, the first opaque wall 131 maysurround the first integrated optical device 101, while leaving anopening for at least one waveguide, e.g. openings 141, 142 for the input151 and output 152 waveguides, respectively. The term “surrounds” isunderstood herein as allowing for openings in a surrounding structure ifrequired, e.g. the openings 141, 142 are provided in the first opaquewall 131 for the input 151 and/or output 152 waveguides.

Referring specifically to FIG. 1B, the light shield structure 108 may benot coplanar with the first integrated optical device. In the embodimentshown, the light shield structure 108 does not extend to the plane ofthe first integrated optical device, being farther away from thesubstrate 150 than the first integrated optical device. This may beadvantageous in embodiments where the light shield structure 108includes a metal structure, and the first integrated optical device 101includes a semiconductor structure under the metal. The light shieldstructure 108 may also be closer to the substrate 150 than the firstintegrated optical device 101. The light shield structure 108 mayinclude not only an opaque absorptive structure but also nano- andmicrostructures such as a photonic crystal, a plasmonic structure, or arandom or semi-random scatterer, for example.

In some embodiments of the present disclosure, at least one of the first101 and/or the second 102 integrated optical device may be manufacturedon additional substrates bonded to the substrate 150. Alternatively, atleast one of the first 101 and/or the second 102 integrated opticaldevice may be monolithically fabricated on the substrate 150.Furthermore, in some embodiments, the first integrated optical device101 may include a light emitting device such as a laser or asemiconductor optical amplifier (SOA) e.g. a reflective SOA and/ortraveling-wave SOA, while the second integrated optical device 102 mayinclude a receiver, a photodetector, etc.; or the other way around. Thefirst 101 and/or second 102 integrated optical devices may be comprisedof Si, SiO₂, doped glass, SiON, SiN, InP, AlGaAs, GaAs, InGaAsP, InGaP,InAlAs, and InGaAlAs. By way of a non-limiting example, the substratemay include Si, GaAs and InP.

Referring to FIG. 2, a photonic integrated circuit 200 is a variant ofthe photonic integrated circuit 100 of FIGS. 1A and 1B, and includessimilar elements. The photonic integrated circuit 200 of FIG. 2 includesa metal wall 231. The metal wall 231 (only one half is shown in FIG. 2for clarity) may be disposed on the same layer as the first integratedoptical device 101 and may surround the first integrated optical device101. A metal layer 113 may be disposed on top of the metal wall 231 overthe first integrated optical device 101, for extra protection againststray light.

In accordance with one aspect of the present disclosure, an integratedphotodetector of a photonic integrated circuit may be optically shieldedusing an opaque wall structure made of the very material aphotosensitive layer of the integrated photodetector is made of,although a doping level may be adjusted for better absorption of light.Referring to FIG. 3, a photonic integrated circuit 300 is a variant ofthe photonic integrated circuit 100 of FIGS. 1A and 1B, and includessimilar elements. The photonic integrated circuit 300 of FIG. 3 includesan optically absorbing wall, e.g. a semiconductor opaque wall 331surrounding the first integrated optical device 101 and shielding thefirst integrated optical device 101 from exterior light 309. In oneembodiment, the semiconductor opaque wall 331 is made of germanium. Inanother embodiment, the semiconductor opaque wall 331 is made of silicondoped to a carrier concentration of at least 10¹⁸ cm⁻³. Preferably, thesemiconductor opaque wall 331 should have optical transmission of lessthan 10%, and more preferably less than 5% of the incoming stray light309.

Turning now to FIGS. 4A and 4B, an integrated photodetector 400 of thepresent disclosure includes an isolating silicon substrate 402 includinga buried oxide layer 403 on a silicon underlayer 401, a slab opticalwaveguide 421, and a photosensitive slab 422 optically coupled to theslab optical waveguide 421. A first electrode 431 may be electricallycoupled to the photosensitive slab 422 for conducting a photoelectricsignal provided by the photosensitive slab 422 upon illumination withlight guided by the slab optical waveguide 421. The first electrode 431may encircle or surround the photosensitive slab 422 as shown in FIG.4B, thus functioning as a light shield for absorbing or reflecting straylight 409 propagating towards the photosensitive slab 422. A secondelectrode 432 may be disposed on top of the photosensitive slab 422,thus shielding the photosensitive slab 422 from ambient light 488.

FIGS. 4A and 4B illustrate but one example of an electrode structurehaving direct current (DC) or radio frequency (RF) electrodes configuredfor usage as light shields. More generally, an optical device may beshielded by surrounding light-emitting or light-sensitive portions ofthe optical device with an electrode structure of the optical device,e.g. photodetector electrodes, modulator electrodes, etc.

Referring to FIG. 5, a photonic integrated circuit 500 is an embodimentof the photonic integrated circuit 100 of FIGS. 1A and 1B, and includessimilar elements. The photonic integrated circuit 500 of FIG. 5 includesa substrate 502 and a first opaque wall 531. The photonic integratedcircuit 500 further includes a waveguide Y-junction 521 (FIG. 5) as anembodiment of the first integrated optical device 101 (FIG. 1B). Thefirst opaque wall 531 (FIG. 5) of the photonic integrated circuit 500may surround the waveguide Y-junction 521, e.g. by repeating the shapeof the waveguide Y-junction 521 to capture any light coupled intoradiative modes.

Turning to FIG. 6, a photonic integrated circuit 600 is anotherembodiment of the photonic integrated circuit 100 of FIGS. 1A and 1B,and includes similar elements. The photonic integrated circuit 600 ofFIG. 6 includes a substrate 602 and a first opaque wall 631. Thephotonic integrated circuit 600 further includes an edge coupler 621.The edge coupler 621 (FIG. 6) may be disposed proximate an edge 607 ofthe substrate 602. The first opaque wall 631 partially surrounds theedge coupler 621, leaving the edge 607 available for coupling an opticalbeam 680 to the edge coupler 621 via an optional external lens 682. Awaveguide 651 is coupled to the edge coupler 621. The waveguide 651extends through an opening 641 in the opaque wall 631 for outputting thecoupled optical beam 680.

Referring to FIG. 7, a photonic integrated circuit 700 is yet anotherembodiment of the photonic integrated circuit 100 of FIGS. 1A and 1B,and includes similar elements. The photonic integrated circuit 700 ofFIG. 7 includes a substrate 702 and a first opaque wall 731. Thephotonic integrated circuit 700 further includes a grating coupler 721for optically coupling to an external optical fiber or waveguide, notshown. The grating coupler 721 (FIG. 7) corresponds to the firstintegrated optical device 101 (FIG. 1B). The first opaque wall 731surrounds the grating coupler 721. The first opaque wall 731 has anopening 741 to pass through a waveguide 751 optically coupled to thegrating coupler 721. In the embodiment shown, the waveguide 751 includesserpentine structure including a plurality of alternating turns 781. Atleast one turn 781 may be provided.

First 771 opaque side walls and second 772 opaque side walls may beprovided, as a part of an optical shield structure. The first 771 opaqueside walls and second 772 opaque side walls run on both sides of theserpentine structure, so that first 771 opaque side walls and second 772opaque side walls may absorb or redirect scattered light emitted by thewaveguide 751. The first 771 opaque side walls and second 772 opaqueside walls may provide better stray light capturing than straight walls.Furthermore, a second opaque wall, not shown, may be disposed on thefirst opaque wall 731, and/or on the first 771 and second 772 opaqueside walls.

Referring now to FIG. 8, a photonic integrated circuit 800 is yetanother embodiment of the photonic integrated circuit 100 of FIGS. 1Aand 1B, and includes similar elements. The light shield structure of thephotonic integrated circuit 800 of FIG. 8 includes a Bragg structure 871on a substrate 802. The Bragg structure 871 is configured forout-coupling stray light. The Bragg structure 871 may include aplurality of concentric or parallel walls in the first layer surroundingan integrated optical device 820, as shown.

Turning to FIG. 9, a photonic integrated circuit 900 is yet anotherembodiment of the photonic integrated circuit 100 of FIGS. 1A and 1B,and includes similar elements. The photonic integrated circuit 900includes a substrate 902, which includes a first dielectric layer 911,such as silicon oxide, for example, on the substrate 902. The photonicintegrated circuit 900 further includes of an integrated optical device908. The integrated optical device 908 is disposed between the firstdielectric layer 911 and a second dielectric layer 912. A channel 990extends through the second dielectric layer 912, surrounding theintegrated optical device 908 for absorbing or redirecting stray light.To improve stray light rejection, a metal wall 991 may be formed in thechannel 990. The metal wall 991 may extend through the second dielectriclayer 912 running around the integrated optical device 908. To furthersuppress optical crosstalk and reject stray light, a metal overlayer 992may be disposed over the integrated optical device 908. For better straylight rejection, the metal wall 991 may extend upwards to the metaloverlayer 992.

Referring now to FIG. 10, a photonic integrated circuit 1000 is avariant of the photonic integrated circuit 100 of FIGS. 1A and 1B, andincludes similar elements. The photonic integrated circuit 1000 of FIG.10 may include a SOI substrate 1002 including a buried oxide layer 1003on a silicon underlayer 1001, and first 1021 and second 1022 integratedoptical devices fabricated on the SOI substrate 1002. An opaque wall1031 extends between the first and 1021 second 1022 integrated opticaldevices for suppressing optical crosstalk between the first 1021 andsecond 1022 integrated optical devices. Similar to the photonicintegrated circuit 900 of FIG. 9, the photonic integrated circuit 1000of FIG. 10, may include a metal overlayer 1092 over the integratedoptical device 1021 and 1022. For better stray light rejection, theopaque wall 1031 may extend from the substrate 1002 to the metaloverlayer 1092.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments andmodifications, in addition to those described herein, will be apparentto those of ordinary skill in the art from the foregoing description andaccompanying drawings. Thus, such other embodiments and modificationsare intended to fall within the scope of the present disclosure.Further, although the present disclosure has been described herein inthe context of a particular implementation in a particular environmentfor a particular purpose, those of ordinary skill in the art willrecognize that its usefulness is not limited thereto and that thepresent disclosure may be beneficially implemented in any number ofenvironments for any number of purposes. Accordingly, the claims setforth below should be construed in view of the full breadth and spiritof the present disclosure as described herein.

What is claimed is:
 1. A photonic integrated circuit comprising: asubstrate; a first integrated optical device comprising a slab opticalwaveguide, a photosensitive slab extending from and optically coupled tothe slab optical waveguide, and at least one input/output waveguide overthe substrate; and a metal, light-shield structure surrounding thephotosensitive slab, extending from the slab optical waveguide higherthan the photosensitive slab and capable of shielding the slab waveguidefrom stray light from adjacent optical devices; wherein the metal,light-shield structure comprises a first electrode electrically coupledto the slab optical waveguide for conducting a photoelectric signaltherefrom; and a second electrode on top of the photosensitive slab forshielding the photosensitive slab from stray light.
 2. The photonicintegrated circuit according to claim 1, further comprising a secondintegrated optical device over the substrate adjacent to the firstintegrated optical device with the metal, light-shield structuretherebetween.